The present invention relates generally to a vehicle power window lift motor control system and, more particularly, to a circuit for protecting the motor and its drive circuitry from damage due to overcurrent when the motor is stalled.
Vehicle power window lift motor systems are used to move vehicle windows up and down between two positions or to some point therebetween. Generally, the window continues to move in the designated direction so long as the actuating switch is held. The addition of an "express down" feature to many modem vehicle power window circuits additionally provides continuous window movement in the down direction without requiring more than a quick depression of an "express down" switch or a further depression of the down switch. When the circuit is in the express down mode, window movement continues until either an "up" or "down" switch is actuated, or until an end of travel limit is sensed.
To protect the window lift motor and its drive circuitry from overheating during potentially damaging prolonged motor stall conditions, such as when an end of travel limit has been reached, these systems usually include an overcurrent detection system for interrupting the flow of electric current to the motor whenever the motor current rises above a predetermined threshold or reference current level. The reference level is typically selected empirically taking into consideration the current and/or power capacity of the motor and its drive circuitry. However, it is oftentimes difficult to select a single fixed threshold which is effective over all operating temperature ranges and in the presence of varying circuit conditions.